Photoelectrostatic copier



July 14, 1970 L. E. S-HELFFO 3,520,604

PHOTOELECTROSTATIC coPIER Filed Oct. 16, 1967 4 Sheets-Sheet 3 f wenior: loren/ Zffiieflfr @m fim, w

July 14, 1970 L. E. SHELFFO PHOTOELECTROSTATIC COPIER 4 Sheets-Sheet 4 Filed Oct. 16,, 1967 1101c; E slfelffo United States Patent 01 fice 3,520,604 Patented July 14, 1970 3,520,604 PHOTOELECTROSTATIC COPIER Loren E. Shelffo, Palatine, Ill., assignor to Addressegraph-Multigraph Corporation, Mount Prospect, lll., a corporation of Delaware Filed Oct. 16, 1967, Ser. No. 675,646 Int. Cl. G03g /22 U.S. Cl. 35516 14 Claims ABSTRACT OF THE DISCLOSURE A photoelectrostatic copying apparatus equipped with a reusable continuous belt coated with an organic photoconductive medium adapted to move in an orbital path. A series of processing stations are located adjacent the path of movement of the belt so that, in sequence, it moves past charging, exposing, developing and transfer stations producing a copy or multiple copies on plain paper. The organic photoconductive medium is reusable. -It is ready immediately after a developed image is transferred to the copy sheet to receive a new image without preliminary mechanical or electrical cleaning of the photoconductive medium. The belt is carried on cantilever supported rollers with the processing stations on the outside of the belt path to permit easy removal or replacement of the belt.

BACKGROUND OF THE INVENTION This invention relates generally to a simplified photoelectrostatic copying apparatus and more particularly to an apparatus equipped with a continuous belt coated with an organic photoconductive medium capable of transferring developed material images thereon to another surface.

Photoelectrostatic techniques for making single copies of the graphic original on a treated or coated paper are well known. These techniques are described in an article entitled Electrofax Direct Electrophotographic Printing on Paper, by C. J. Young and H. G. Greig, R.C.A. Review, vol. 15, No. 4, pp. 469-484, December 1954. The basic Electrofax process involves the steps of applying a blanket electrostatic charge on the coated side of the paper while in the dark, exposing the charged surface to a pattern of light and shadow in order to form a latent electrostatic image on the photoconductive surface of said paper, the image then being developed by applying electrostatically attractable pigmented resin powder. This process has been eminently successful in producing copies directly on a flexible substrate, usually paper, which has been coated with photoconductive zinc oxide particles dispersed in a film-forming insulating resin binder. In the circumstance where multiple reproductions of a graphic original were required the complete process, including all steps, 'were repeated for each reproduction.

Other known techniques for electrostatic copying are based on the use of elemental selenium as the photoconductive medium on which a latent electrostatic image is produced, developed with suitable electroscopic powder, and the powder image is then transferred to an untreated surface, such as plain paper, where it is then fixed by such known techniques as heat fusion or solvent vapor fixing. Subsequent use of the selenium medium requires that the old image be removed or erased, whether it be the same image or a new image, before the next image is created on the selenium surface. Here again, multiple reproductions are achieved by repeating the full cycle for each image transferred. The known apparatus for carrying out the above described photoelectrostatic copying processes are quite complex. Depending on whether a photoconductive metallic ion containing crystalline compound, such as zinc oxide, is employed or elemental selenium, there are certain inherent disadvantages in the photocopying apparatus.

In these differing systems, those which employ zinc oxide as the photoconductive medium, suffer from the deficiency that their surfaces are not reusable. The photoconductive member will accept an image from which one or multiple copies may be prepared by various duplicating techniques such as are fully described in the copending application of Loren E. Shelffo, U.S. Ser. No. 632,819, and assigned to the same assignee as the instant application. The same photoconductive member, once the form of the electrostatic image has been developed into a material image, cannot be reused to accept a different form of material image. In other words, the photoconductive medium has to be replaced with a fresh surface.

Reproduction apparatus based on the use of elemental selenium formed into a photoconductive drum will accept different forms of a material image on the same surface but require the intervening step of erasing or otherwise cleaning either mechanically or electrically any trace of the previous image before proceeding to the next imaging step. The step of removing the image requires the use of complex mechanisms and generally renders the equip ment costly both from the manufacturing and maintenance aspects.

Apparatus employing the basic photoelectrostatic process for duplicating multiple copies of a single graphic original are known. Transfer techniques involving the use of a photoconductive drum, prepared by the vapor deposition of elemental selenium on a metal drum, require that the photoconductive surface be cleaned or the image otherwise erased after each transfer before the next image can be put on.

Duplicating techniques utilizing an inorganic photoconductive metal ion containing crystalline material as the photoconductive medium can be accomplished by establishing an image receiving medium on the photoconductive surface in the form of a latent electrostatic image and then successively developing and transferring a powder image to the copy sheet. The development and transfer of the material image from the photoconductive medium can turn out as many as 2000 copies, but, if copies of another original are to be duplicated, a new photoconductive medium has to be used.

There is a need in the photoelectrostatic art for a simplified, low cost, service free, copier-duplicator that can make one copy from each of a number of different originals or hundreds of high quality reproductions of the same original consistently from a photoconductive medium that is reusable.

SUMMARY OF THE INVENTION In accordance with this invention apparatus is provided capable of making copies from a given original by the transfer of a material image, or copies of different originals without replacing the photoconductive medium or without cleaning or otherwise erasing the photoconductive medium between successive transfers.

The photoconductive medium is formed on the surface of a drum or into a continuous belt and stretched over a series of drive rollers so that it moves in a predetermined path that may be oval in configuration or a generally circular path. The precise form, whether it be a belt or a drum, is not critical only that it move in an orbital manner so that the various instrumentalities that give rise to the copy making function can be disposed in a planetary fashion adjacent its photoconductive surface.

The belt is comprised of a conductive base support which may be paper, which has been rendered conductive, or a plastic film such as polyethylene terephthalate, cellulose acetate, vinyl acetate, polyethylene, or other plastic materials which may be formed into a film and rendered conductive either chemically or by metallizing the surface, or the substrate may be made of any metal foil. To one surface of the conductive base support is applied a uniform coating of a photoconductive material which is of the class of organic photoconductors.

It has been found that organic photoconductive materials give surprising results because of their ability to transfer substantial quantities of the developed material image to the receiving sheet. The ability to transfer most of the powder image obviates the need for removing the powder at the end of one cycle prior to the beginning of another so that the presence of the powder does not act as a light barrier and interfere with the formation of subsequent images. The image that is transferred is of high density and generally of good quality.

Another feature of organic photoconductive systems is their ability to rapidly become dark adapted, i.e., the material does not undergo photoconductive fatigue after being charged and exposed repeatedly in rapid succession. These materials exhibit the ability to accept a saturation charge which will be equivalent to its dark adapted condition under a rapid cycling mode of operation with corresponding good dark decay and light decay characteristics. This is important in copier-duplicator apparatus where the photoconductive medium undergoes charging and exposure in rapid succession. Each new cycle requires that the photoconductive medium accept a saturation charge level in a large number of successive cycles equivalent to when the photoconductive medium is in a dark adapted condition. Hence, the material lends itself to reusability.

A recognized deficiency of these materials is their slow photo response when compared to zinc oxide-resin binder systems and selenium. As will be described in greater detail hereinafter, the apparatus and method of the instant invention permits the utilization of the most desirable portion of the light decay characteristic curves of these materials by applying a potential to the developer means that are employed for applying the transferable image.

Such photoconductors may be selected from a wide range of aromatic hydrocarbons such as disclosed in U.S. Pat. 3,287,199 to Helmut Hoegl et al., issued Nov. 22, 1966. Such photoconductors include aromatic hydrocarbons such as naphthalene, anthracene, benzanthrene, chrysene, p-diphenylbenzene, diphenyl anthracene, p-terphenyl, and p-quaterphenyl, and sexiphenyl; heterocyclic compounds such as oxadiazoles; triozoles; imidazolones and imidazol'thiones; N-aryl pyrazolines; hydrated imidazoles; and other compounds. The organic photoconductive substances may be applied to the base support from a solvent solution or in conjunction with a film forming binder such as a natural resin such as shellac; a synthetic resin such as coumarone resin, or such binders as cellulose ethers, vinyl polymers, polyacrylates, isobutylene, polyethylene and chlorinated rubbers.

Another group of photoconductors are organic polymeric photoconductive materials. The classes of polymeric substances that have been found to be useful in the apparatus of the instant invention are vinyl polymers, and more particularly carbazole and vinyl copolymers containing vinyl carbazole units. In the circumstance where the photoconductor is an organic polymeric material, it will serve as its own film forming agent and will not require the use of a separate binder. However, in some instances it may be desirable to add a resin to the polymeric organic photoconductive materials.

The organic photoconductive media may be sensitized to increase its photo response by including additives such as 1r-complex acids which are disclosed in detail in US. Pat. 3,037,861, to Helmut Hoegl et al., issued June 5, 1962.

The belt is stretched around a series of drive rollers to form a continuous loop with the photoconductive surface facing outward from the center of the loop. The instrumentalities necessary to create a transferable material image from the belt surface are disposed along the path of movement of the belt at various stations. One of the belt drive rollers is connected to a main drive motor to move the belt along the predetermined path, and the rollers are cantilever supported to facilitate easy removal of the belt.

At the first station there is provided a charging means for imparting a blanket electrostatic charge to the photoconductive layer. A source of charge emission juxtaposed the belt surface spraying charges uniformly over the belt surface as it passes underneath the source. Such a charging device may be in the form of a conventional corona emission wire operating against a ground plane or a pair of opposing corona emission electrodes of opposite polarity.

The charged belt by virtue of its electrostatic charge is now sensitive to electromagnetic radiation and the drive means brings it to a second station where a pattern of light and shadow is cast upon the charged surface to create a latent electrostatic image. The exposure station may be equipped with an optical system in order to project the pattern onto the charged surface or optionally may provide for contact exposures by bringing the original subject into contiguous contact with the charged surface and then directing radiation onto the assemblage. In the circumstance that the belt is transparent, a further option is available for effecting a contact print bythe reflex technique whereby the radiation is directed onto the base support side of the belt. To accomplish this, a radiation source is mounted within the loop at the second station.

At the second station the photoconductive belt is stretched between drive rollers so as to present a fiat planar surface which can function as an exposure plane either for contact printing or projection imaging.

Leaving the second station, the belt moves to the third station at which a toner is applied to the latent image-bearing photoconductive surface. The developer construction provided in the instant invention is of the conventional magnetic brush-type applicator. It has been found desirable that the magnetic brush-type construction be connected to a source of direct current potential having the same polarity as the latent electrostatic image so as to provide a field between the latent image and the brush-like formation of the developer mix. The establishment of a field between the brush and the charge image requires the developer apparatus to be electrically insulated from the rest of the machine, that is, electrically floating. Any residual toner in the background areas remaining on the surface from the previous cycle is reattracted onto the brush. In this way the accumulation of toner from one run to the next is eliminated.

The toner is selectively attracted to the charge image producing a transferable material image on the organic photoconductive medium.

The material image-bearing surface of the belt is next conveyed to the fourth station where a transfer roll is in pressure contact with one of the belt drive rolls with the belt passing between the nip of the rollers, included in the structure of the fourth station is a supply of imagereceiving copy sheets which are fed in timed relation with the image-bearing portion of the belt between the transfer roll and the belt. The pressure roller set preferably should provide a resilient roller in pressure contact with a hard surface roller with either the transfer roll or the belt drive roll having the resilient surface.

The control of the amount of pressure exerted at the transfer station is significant when utilizing equipment in the duplicating mode, which involves making transfers from the same latent image, and accordingly the transfer roll is adjustable mounted permitting uniform setting of the roller position from end to end in order to produce the required pressure at the transfer station.

As the copy material exits from the transfer station it is passed through a fuser where the transferred powder image is fixed by heat, pressure or solvent vapors.

It is desirable to provide an electrical field at the point of transfer between the material image and the copy sheet. This field operating in conjunction with the controlled pressure is important to the success of the duplicating mode of operation.

As each increment of the photoconductive medium leaves the transfer station, it is automatically in condition to be reprocessed, i.e., either using the undisturbedlatent electrostatic image or to again receive a blanket electrostatic charge to render the photoconductive medium sensitive to electromagnetic radiation. I

It is a general object of this invention to provide a compact, economical photoelectrostatic copying apparatus that is greatly simplified in its construction and operation and capable of producing high quality reproductions on plain paper.

It is another object of this invention to provide a photoelectrostatic machine that is compact, low cost, high speed, and produces high quality copies on plain paper capable of making a single copy from a number of difierent originals or multiple copies from one original by a transfer technique.

It is yet another object of this invention to provide a photoelectrostatic machine capable of making a single copy or multiple copies either by contact printing or projection printing on plain paper.

It is yet another object of this invention to provide a photoelectrostatic machine equipped with an organic photoconductive medium that is capable of producing a single copy or multiple copies simply and economically by transfer to plain paper.

It is a specific object of this invention to provide a photoelectrostatic copying apparatus in which the photoconductive medium is an organic photoconductor formed into a continuous belt that is recycled without cleaning.

It is another specific object of the invention to provide a photoelectrostatic copying apparatus in which a continuous photoconductive belt is carried on cantilever supported rollers to facilitate belt removal without aifecting processing stations mounted in fixed positions around the belt path.

It is yet another specific object of this invention to provide a photoelectrostatic copying apparatus using a continuous photoconductive belt carried on rollers in which the rollers form parts of various processing stations.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be easily understood by reference to the following detailed description and to the drawings in which:

FIG. 1 illustrates the light decay characteristics of the photoconductive materials used in this invention compared to prior art materials.

FIG. 2 is a side view of the apparatus of this invention with the side covers removed.

FIG. 3 is a front view of the apparatus with the cover removed.

FIG. 4 is a side view of another embodiment of the apparatus of this invention.

FIG. 5 is a schematic electrical wiring diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Having reference now to the drawings, and particularly FIG. 1, there is illustrated the light decay curves of an organic photoconductive medium identified as I and I; curve II represents a typical prior art zinc oxide resin binder system which has been dark adapted.

The material depicted in curve I shows a rather rapid drop in voltage upon exposure to light tends to slow down forming a well defined toe portion at the 200- volt level. The toe portion represents the increased amounts of exposure in foot candle seconds to reduce the voltage to a level where there is a greater difference between the image and non-image areas. It will be appreciated that when a photoconductive material, such as an organic containing medium, is said to have a slow response, it refers to the increased amount of exposure represented by the lower portion of the curve to reduce the light struck areas to zero.

It will be recognized that in order to utilize such a photoconductive medium in a high speed copier-duplicator, unduly long exposure would be required to reduce the charge in the light struck areas to a level where they would not attract toner.

A comparison of curve I with curve II will show that much longer exposures may be required with the organic photoconductive medium to expose the non-image area to where its voltage approaches the same zero level as zinc oxide.

It was found that by imposing a potential between the photoconductive medium and the developer the voltage level on the photoconductive medium represented by the toe portion need not be dissipated to zero by exposure to electromagnetic radiation. In the circumstance that the material was exposed for T foot candle seconds, the selected light struck areas would be at a corresponding voltage level V which would attract toner. Upon the application of a potential V to the developer proper at the same polarity and at a level equal to or slightly greater than the residual potential V the light decay curve behaves as if it has been shifted to the position shown by the dotted line curve I. By applying a potential V to the conductive substrate while keeping the developer at ground there is provided the same control over the amount of exposure required. In the latter case the polarity is opposite in sign to the cargo image and again the potential must be at least equal to charge level in the background and up to volts less than the charge image.

The organic photoconductor can be charged over a range of from 100 volts to 1200 volts, the preferred range being from 300 volts to 800 volts. The background voltage may range from 50 volts up to within 100 volts of the charge image. The potential provided between the developer and the photoconductive medium must be equal to or slightly greater than the voltage in the background area.

Referring again to FIG. 1 and curve I in particular, the effect of this control potential may be illustrated by examining the performance of a typical organic photoconductive medium such as polyvinyl carbazole. The medium is charged to a level of 775 volts. From the curve it can be seen that it would require an exposure in excess of 60 foot candle seconds to reduce the voltage in the background area to a level of 50 volts or less where it would no longer attract toner. In carrying out the objects of this invention, the exposure is reduced by varying either time or intensity to the point along the curve where the voltage is about 275 volts. This would require an exposure of about 15 foot candle seconds. In order to negate the high voltage level in the background, a potential is provided at the developing site equal to 275 volts or greater. In the instant example the voltage was about 290-300 volts. If the potential is applied to the magnetic brush, it is the same sign as the charge image and if applied to the conductive support, it is opposite in sign. The effect of such a control potential is to permit the use of the photoconductive member in the portion of the curve with the greatest slope and, hence, give the effect of having shifted the curve to the dotted line position 1'.

Another feature of this instant apparatus and method is the ability to recycle the photoconductive medium in rapid succession, producing copies from different originals by transfer without an accumulation of toner such that a separate mechanical or electrical means of cleaning the surface between cycles is not required. As pointed out hereinabove, the organic photoconductors in the proper environment have been found to substantially transfer the material image. Understandably, some of the toner will not transfer adhering in the image and background areas at the conclusion of a cycle. The amount that remains, however, does not interfere with the charging or exposing steps.

Surprisingly, there is no accumulation of toner after successive cycles, as would be expected, and it is believed that any remaining toner is recovered in the developer simultaneously with the development of a new image. The exact explanation for this recovery of toner is not fully understood, however, it is believed that the loosely adhering toner is readily attracted to the developer. As a result of this control over the toner from one cycle to the next, the belt remains substantially free of toner to the extent that high quality images free of background are transferred at the end of each cycle and the next cycle has available a photoconductive medium free of toner that may interfere with charging and exposure of a new image.

Referring to FIGS. 2 and 3, there is illustrated a copy machine 10 constructed in accordance with the present invention. The copy machine 10 is of the photoelectrostatic type enclosed in a cabinet or housing 12, an infeed station 14 into which are fed the originals to be reproduced. At the lower portion of the housing there is provided a stack supply of cut sheets 16 from which are fed the copy sheets to which are transferred the powder images. The copy sheet passes through a fixing station 18 and emerges into a copy receiving tray 20 at the front of the housing 12.

Within the central portion of the housing is the photoconductive medium identified generally as 22. The photoconductive medium comprises a continuous belt 24 having applied to the surface thereof a photoconductive coating or layer 26. The continuous belt is stretched about a plurality of rotatable rolls 28, 30, 32, and 34 which are mounted for rotation about horizontal parallel axes a, b, c, and d, respectively. One of the rolls, such as roll 34, is swingably mounted on two bracket members 36, and is designed for yieldably biased displacement away from the belt path to serve as a belt tensioning control. Another of these rolls, for example roll 30, is caused to be positively rotated through shaft b, by suitable driving mechanism contained within the housing 12.

The tensioning roll 34 is journalled at its opposite end in two swingable arms 37 and 38 which in turn are pivotally mounted by the brackets 36 which are carried on the end plates 40 and 42. The remaining rolls 28, and 32 are journalled directly in the plates 40 and 42. The end plate 42 rises from a base portion 46 of the frame structure 48, while the end plate 40 which receives the other shaft ends for the rolls 28, 30, and 32 is unsupported, giving rise to a cantilever-type mounting for the rollers 28, 30, and 32 and the photoconductive medium 22, so that the belt 24 may be easily mounted and removed through the release of the tensioning roll 34. The arms 37, 38 are yieldably biased by means (not shown) for clockwise rotation (FIG. 2) to tension the belt 24. These arms can be pivoted against the bias to release the tension and permit the belt 24 to be removed by movement along the axes of rotation of the rollers 28, 30, and 32 and over the end plate 40. It will be appreciated that the portion of the belt passing between the rolls is in a fiat planar condition and that the belt coursing over the rolls provides suitable working areas for the various instrumentalities hereinafter described.

Surmounting the photoconductive belt assembly 22 is a swingably mounted superstructure 54 formed of a pair of L-shaped members 56 and 58 hingedly secured to the frame 48 through the fasteners 60 and held in spaced apart relation by the tie bars or rods 62 and 64. The superstructure 54 is swingably mounted to a position overlying the flat portion of the path taken by the belt 24 passing over the rolls 28 and 32.

On the underside of the superstructure 54 is a corona discharge device 70 which includes a fine wire electrode 72 stretched inside the conductive shield 74. The corona discharge device extends between the members 56, 58, being affixed to the tie bar 62. The corona discharge device is mounted in spaced relation from /2 to inch above the organic photoconductive layer 26 as the latter rounds the roll 32. The photoconductive layer 26 is imparted a blanket electrostatic charge at this station.

Included on the underside of the superstructure at the portion spanning the rolls 28 and 32 are a pair of rotatable rolls and 82 mounted for rotation about the shafts e and which, in the portion shown in the drawings are parallel to the shafts a and c and reside inside the lateral dimension between the rolls 28 and 32 extending over the full width of the belt 24. The belt, as it courses between the two sets of rolls 28, 32 and 80, 82 is supported from below and above, respectively, to provide a taut, fiat optical exposure plane 84. A pair of elongated radiation sources 86 and 88 are supported in suitable reflector housings 90 and 92 which straddle the belt and extend the width thereof providing the option of irradiating the photoconductive layer 26 either through the belt or directly from above. The reflector housings are mounted respectively in the cutout portion 94 and 96 provided in the superstructure and the end plates 40 and 42 through bracket members 98 and 100. The roll arrangement also serves to bring the original which is to be reproduced into intimate and contiguous contact with the photoconductive layer 26 over the entire exposure plane 84.

In operative association with the roll 28 is the developer assembly 104 for applying the electroscopic powder to the latent image-bearing photoconductive layer 26 as it leaves the exposure station. The developer assembly includes a trough 106 in which is contained a supply of developer powder which can be a conventional mixture 108 of iron carrier particles in an electroscopic thermoplastic powder of the type used in magnetic developers. The construction and operation of magnetic brush developers are well known and will not be discussed in detail here. -It has been found necessary in the mounting of the developer assembly described hereinbefore that it be electrically floating, i.e., insulated from the rest of the apparatus. The trough is supported on a shelf or platform 110 comprised of a highly insulating plastic material, such as acrylic or polystyrene resins or the equivalent, which in turn is supported by the frame structure 48. The metal trough is connected to the negative terminal of a DC voltage supply and the other terminal of the supply being connected to ground. It has been found desirable to apply a negative potential to the developer in the range that is equal to or slightly greater than the voltage in the background area.

It will be appreciated that the application of the developer powder has been described in terms of a magnetic brush assembly; other types of powder development may be used, such as, for example, a cascade development using conductive glass beads.

Transfer of the material image to the copy sheet is accomplished at the transfer station at which a copy sheet 16A is fed from the supply stack 16 by means of feed wheel 121 in timed relation to the arrival of the image at the transfer station. In pressure contact with the roll 30 is a transfer roll or pressure assembly 124 which causes the powder image to transfer to the copy sheet 16A. The transfer roll 124 operating in conjunction with the roll 30 -will cause the powder to transfer to the copy sheet. The transfer roll (FIG. 3) is journalled for rotation in an insulating bearing 122 which in turn is received in a pivotable yoke 126 which is aflixed to the upright 128 and 130 through pivoting connections 132 and 134. The yoke is supported at its front end by an adjustable plunger 140 urged against the yoke by a coiled spring 142 which surrounds the body of the plunger, one end of the plunger being received in a sleeve member 136 having an outside thread (not shown). The spring is compressed between a threaded nut 144 threaded on the sleeve and a shoulder 146 at the head portion of the plunger. The body of the sleeve which is adapted to receive one end of the plunger has markings 150 scaled in plus or minus fractions of an inch on either side of a zero position to indicate the location of the plunger therein as measured against the bottom edge of theadjusting nut 144. When the adjusting nut is at the rollers are just touching; when lined up with a minus reading the plunger is moved deeper into the sleeve and rolls 30 and 124 are apart; and a plus reading represents the amount of compression of the rubber roll 124 and, hence, a decrease in its radius at that point. The nut 144 can be moved to a setting in which the roller 124 is spaced from the belt 24 to permit removal of this belt in the manner described above.

Greater or lesser pressure between the transfer roll 124 and the roll 30 is achieved by increasing or decreasing the compression of the spring. During the copy making mode the pressure may range from 2 pounds to 100 pounds per lineal contact inch. One advantage of the spring biased support is its yieldability to abnormal or unusual thicknesses of paper going through the rolls, thereby avoiding'damaging either the transfer roll 124 or the roll 30.

In the circumstance that the apparatus is to be operated in the duplicating mode, i.e., where the material image is transferred from the photoconductive surface and thereafter the latent image is successively redusted and transferred, it becomes necessary to apply a field between the surface of the powder image and the plain paper which is fed from the stack 16. To create the proper environment for the duplicating mode, a DC voltage is applied to the transfer zone by connecting the metal shaft 148 to a DC supply applying a field having a polarity which is the same as the polarity of the electrostatic charges in the latent image portions. The transfer roll preferably is made of a conductive rubber having a resistivity in the range of from -10 ohm-centimeters. The voltage applied to the conductive core of the roll 124 is in the range of from 1000-3000 volts, preferably in the range of from 1200-2000 volts, and the pressure in the range of from 2 pounds of 8 pounds per square inch contact area.

The stack supply of copy sheets 16 is located generally beneath the shelf 110 having a feeder wheel 121 frictionally engaging the uppermost sheet in the stack. The feeder wheels are driven from the main drive motor to feed a feed a copy sheet for arrival at the transfer station in timed relation with the arrival of the powder image thereat.

It will be appreciated that a roll feed could be used to equal advantage in the instant apparatus in conjunction with a suitable cutting means for severing the copy sheet once the image has been transferred thereto.

Referring to FIG. 4, there is shown another embodiment of the apparatus of this invention, identified generally as 160, in which the exposure of the photoconductive surface is accomplished using an optical system to project a pattern of light and shadow produced by i1- luminating an original held on a flat transparent platen.

The apparatus 160 employing projection optics is similar in construction with respect to the processing instrumentalities to the apparatus hereinabove described with the exception of the exposure station.

Within the framework 161 is a photoconductive medium 22, comprising a continuous belt 24 stretched about a plurality of rotatable rolls 28, 30, 32, and 34. The belt' tensioning roll 34 is pivotally mounted on the end plates 40 and 42.

Surmounting the photoconductive medium is an optical assembly 162 for projecting a pattern of light and shadow on that portion of the belt passing between the rolls 28 and 32 which functions as an exposure plane 164, said assembly including a light-tight enclosure 166 having supported therein a lens element 168. The top portion of the enclosure 166 is equipped with a window opening 170 upon which is received the original subject to be reproduced.

Adjacent the underside of the window 170 within the enclosure 166 are a pair of elongated radiation sources 172 mounted in suitable reflectors 174 to properly illuminate the original and produce a pattern of light and shadow which is then received into the lens 168 and thence projected onto the organic photoconductive layer 26 at the exposure plane 164.

The corona discharging device 70 is mounted on extensions of the upright frame structure 48 being secured to the structural cross piece 176 in position juxtaposed the photoconductive surface of the belt as it passes over roll 32.

The developer construction of the developer assembly 104 and the operation and construction of the transfer station 120 have been full described hereinabove in connection with FIG. 2.

The electrical controls of the apparatus of FIG. 2 of this invention are represented by the wiring diagram of FIG. 5 showing the feed lines 180 and 182 connected across a 115-volt AC supply which feeds three control circuits generally identified at 184, 186, and 188 representing respectively the illumination control, developer and main drive control, and the high voltage power circuit.

The main switch 190 is connected in line 180 which, in its closed condition, provides 115 volts AC to the variable resistance 192 connected directly across the feeder lines. The output of the variable reactance control supplies power to the fluorescent tube 86 equipped with the conventional ballast 196 and starter 198 which is energized upon closing switch 200. The center tap 202 of the variable reactance control 192 provides a voltage supply to the quartz lamp 88 which is energized upon closing switch 206.

The drive control circuit 186 is powered by a DC power supply 208 connected across the feeder lines to the power supply 208. The main drive motor 212 is connected by conductors 214 and 216 to the supply 208 which drives the roll 30 through a suitable belt drive 209. The developer motor 219 is connected to the supply 208 through conductors 220 and 216.

The high voltage power supply circuit 188 includes separate power supplies 224, 226, and 228 which are connected across the feeder lines. The supply 224 provides a variable voltage to the developer assembly 104 through a resistance 230 (25 megohms), supply 228 provides voltage to the charging device 70, and supply 226 provides the voltage to the transfer roll 124 through a resistance (25 megohms.)

In operation the apparatus is turned on by closing contact 190 which applies 115 volts to the high voltage power supplies 224, 226, 228 which supply the developer, transfer roll and the corona discharge. The power supplies to these instrumentalities remain energized during operation.

At the same time the drive motors 219 and 212 are energized through normally closed contacts 218 and 222 so that the belt moves past the various stations.

The operator next selects the mode of exposure which may be by contact or projection and in the former case the exposure may be through the original by the lamp 86 or through the transparent base support in which case lamp 88 must be energized. The selection is made by closing switch 200 for energizing lamp 84 or switch 206 for turning on lamp 88.

The lamp selected remains energized in order that the portion of the photoconductive medium between exposed areas is discharge so it cannot attract toner. In the projection mode the lamp is turned on only for exposure but a separate lamp is used to clear the charge. Lamps 172 would be used for projection.

The photoconductive medium, prior to advancing to the exposure area, received a first charge level as it passed beneath the corona wire 72.

A printed one-side original is fed in at the infeed station 14 and is carried into the nip between the roller 80 and the belt 24. The length of the belt extending 'between rollers 80 and 82 forms a flat exposure and the original is exposed by lamp 86 since a one-sided original is used. The exposed original exits from roll 82.

The surface 26 now has a latent electrostatic image including a second level of potential in the exposed areas and advances to the developer 104 where the image is developed.

As the belt leaves the developing station, a control device (not shown) for the feeder wheel is energized to feed a sheet of paper in timed relation with the image portion of the belt so that both arrive at the transfer station in alignment to properly locate the image.

The transfer occurs under a pressure setting in the range of from 2 pounds to 100 pounds per lineal contact inch, preferably in the range of from pounds to 50 pounds per lineal contact inch, and thence through the fuser 18 into the copy tray 20.

The medium is then immediately ready for another original.

While the apparatus has been described in terms of a negative corona, it is contemplated that the apparatus and method can be utilized with a positive corona and a reversal developer material while imposing a positive potential to the developer, or a negative potential to the base support.

The invention has been described with some particularity. The use of organic photoconductive systems which exhibit the feature of reusability without fatigue is unique and one skilled in the art may make variations which would come within the scope of the instant invention.

What is claimed is:

1. An apparatus for making copies of originals on copy material comprising:

a supporting frame including a generally upstanding supporting structure,

a plurality of rollers disposed in spaced positions with at least one of the rollers spaced below the other rollers, the rollers being mounted at one end on the structure for rotation about generally parallel and horizontal axes,

a flexible and endless belt mounted on the rollers and having a photoconductive surface facing away from the rollers,

a plate carried by and rotatably mounting the other ends of the rollers, the periphery of the plate being less than the length of the belt,

a tensioning means movably mounted on the frame and normally bearing against the belt to bias the belt into intimate engagement with the rollers, said tensioning means being movable away from the belt to permit the belt to be removed from the rollers by movement along the axes of the rollers and over the plate,

drive means carried on the frame and coupled to at least one of the rollers at said one end of the roller for rotating the roller and moving the belt over a fixed path,

charging means mounted on the frame and disposed along but outside of the path for applying a uniform electrostatic charge to the photoconductive surface of the belt,

exposing means mounted on the frame and disposed along but outside of the path spaced in the direction of movement of the belt from the charging means for selectively illuminating the belt in accordance with the original to be copied to provide a latent electrostatic image,

developing means mounted on the frame and disposed along but outside of the path spaced in the direction of movement of the belt from the exposing means for converting the latent image to a material image, transfer means mounted on the frame along the path spaced in the direction of movement of the belt from the developing means for transferring the material image from the belt to a copy sheet, said transfer means including a pressure assembly movably mounted on the frame opposite a first one of the rollers and normally biased toward this roller to bias copy material and the belt against the first roller, the pressure assembly being movable away from the first roller to permit the removal of the belt from the rollers, and copy material feeding means carried on the frame adjacent the transfer means for feeding copy material from a supply thereof to the transfer means.

2. The apparatus set forth in claim 1 in which the developing means includes a magnetic brush assembly mounted on the frame opposite a second one of the rollers.

3. The apparatus set forth in claim 1 in which the belt includes a conductive layer connected to a reference potential point, the developing means includes electrically conductive applying means for applying a mixture of electrostatically attractable material and electrically conductive carrier particles to the latent image on the belt, and a biasing potential source is connected to the applying means.

4. The apparatus set forth in claim 3 in which the frame is electrically conductive, and insulating means are provided for mounting the developing means on the frame.

5. The apparatus set forth in claim 1 in which the belt includes a conductive layer connected to a reference potential point, the pressure assembly includes an electrically conductive roller means biased toward the first roller, and a biasing potential source is connected to the conductive roller means.

6. The apparatus set forth in claim 5 in which the pressure assembly includes a linkage rotatably mounting the conductive roller means, and means coupled to the linkage for adjusting the position of the linkage and the force with which the conductive roller means is yieldably biased toward the first roller means.

7. The apparatus set forth in claim 1 in which the belt includes a conductive layer connected to a reference potential point, and the charging means is disposed opposite a third one of the rollers.

8. The apparatus set forth in claim 1 including guide means for feeding an original to be copied into a contact with the belt at a point along the path located between the charging means and the exposing means to move with the belt through the exposing means, the original being removed from the belt at a point in the path prior to the developing means.

9. The apparatus set forth in claim 8 in which the exposing means includes lamp means for illuminating the original on the belt.

10. The apparatus set forth in claim 1 in which the frame includes a pivotally mounted assembly carrying the charging means to permit the charging means to be moved away from the path of the belt.

11. In an apparatus of the type described for making reproductions of a graphic original on copy sheets from a reusable photoconductive medium, the combination comprising:

photoconductive belt means stretched about a series of guide rollers for movement in a generally circular path,

tensioning means contacting one surface of said belt means for establishing a planar course over at least two such guide rollers over which said belt is required to pass,

exposure means juxtaposed said planar course,

magnetic brush developing means adjacent said belt at a position beyond said course for developing an image by supplying toner,

charging means directed at said belt at a position prior to said course,

transfer means comprising an adjustable transfer roller electrode adjustable as to one of said guide rollers and in pressure contact therewith for the purpose of adjusting said pressure between said transfer roller and said belt as said belt passes therebetween,

a biasing potential source connected to the transfer electrode,

copy sheet feeding means for feeding a copy to said transfer means to receive said developed image, and drive means for recycling the belt to produce successive copies from different originals.

12. The apparatus set forth in claim 11 including means for applying a voltage gradient between said photoconductive belt and said brush.

13. The apparatus set forth in claim 11 in which the photoconductive belt comprises an organic photoconductive layer applied to a conductive support.

14. In an apparatus of the type described for making reproductions of a graphic original on copy sheets from a reusable photoconductive medium, the combination comprising:

photoconductive belt means stretched about a series of guide rollers for movement in the generally circular path,

tensioning means contacting one surface of said belt means for establishing a contact exposure course between at least two such guide rollers over which said belt is required to pass,

contact exposure means for passing said graphic original in contact with a portion of said belt,

magnetic brush developing means adjacent said belt at a position beyond said last named means for developing an image by applying toner,

charging means directed at said belt at a position prior to said exposure means,

transfer means comprising an adjustable transfer roller electrode adjustable as to one of said guide rollers and in pressure contact therewith for the purpose of adjusting said pressure between said transfer roller and said belt as said belt passes therebetween,

a biasing potential source connected to the transfer electrode,

copy sheet feeding means for feeding a copy to said transfer means to receive said developed image, and

drive means for recycling the belt to produce successive copies from different originals.

References Cited UNITED STATES PATENTS 2,956,487 10/1960 Giaimo 35516 X 3,432,231 3/1969 Gardner 355--16 X 30 JOHN M. HORAN, Primary Examiner 

